The present invention relates to a copier, facsimile transceiver, printer or similar image forming apparatus and, more particularly, to an image forming apparatus capable of removing impurities from a toner collected from the surface of an image carrier by a cleaning unit before the toner is returned from the cleaning unit to a developing unit.
One of image forming apparatuses extensively used today has an image carrier, a developing unit, an image transferring unit, and a cleaning unit. The developing unit develops a latent image electrostatically formed on the image carrier by a toner. The resulting toner image is transferred from the image carrier to a recording medium by the image transferring unit. The cleaning unit collects the toner remaining on the surface of the image carrier after the image transfer. The collected toner is returned to the developing unit by transporting means to be reused. The problem with this type of image forming apparatus is that the toner collected from the image carrier by the cleaning unit contains paper dust and other impurities. Specifically, such impurities are introduced in the toner while the toner is agitated, charged and transferred from a developing roller, or developer carrier, to the image carrier in the developing unit and transferred from the image carrier to the recording medium in the image transferring unit, while the recording medium is separated from the image carrier, and while the image carrier is cleaned after the image transfer, When use is made of a two-component developer, i.e., a mixture of a toner and a carrier, even the carrier exists in the collected toner as an impurity. The impurities admixed with the toner often scratch the developing roller and adversely effect an image when returned to the developing unit together with the toner.